Paraboloids are often used as antenna reflectors attached to satellites. The paraboloid is often used to collect and reflect electromagnetic energy into or out of a "feedhorn" which brings concentrated energy into or out of the satellite.
Two basic designs characterize such reflectors. In a "center fed" design, the feedhorn is mounted directly along the central axis of the reflector. Often, the feedhorn in this design interferes with the incoming or outgoing signals. An alternative design which eliminates this problem is an "offset" design, in which the parabolic reflector is shaped to reflect and concentrate the signal off of the center of the paraboloid, allowing the feedhorn to be placed to one side, out of the way of the signal.
Two basic materials, wire mesh and solid materials, are used in both designs. A wire mesh material is lightweight, but does not reflect as well. For some transmissions, a mesh is impractical. A solid material solves this problem, but can be somewhat heavier than the mesh.
There are competing interests at stake when a paraboloid reflector is sent into space. The larger the reflector, the better its transmission and reception capabilities. However, the diameter of the spacecraft used to launch the reflector can limit its size. It is therefore necessary to pack a paraboloid surface more compactly for transport in the launch vehicle.
While reducing the diameter of the reflector can make its launch feasible, it may not necessarily make the launch cost efficient. Because launch vehicles often hold more than one device, the more compactly the paraboloid is packed, the more devices may be launched in the same vehicle, dramatically reducing costs.
Competing with the goals of practicality and cost is reliability and ease of deployment. Once launched, a collapsed paraboloid must be deployed for use in space. Simpler deployment mechanisms are preferred for their improved reliability. Complex mechanisms are more prone to failure and are thus much less desirable.
In addition, it is highly desirable to employ a mechanism that is simple enough for automatic operation. Not only does such a device allow for deployment from both manned and unmanned launch vehicles, but it also avoids the difficulties and expense of an astronaut, in full space suit, required to deploy alternative designs.
The background art contains several attempts to pack a paraboloid surface more compactly. While such attempts succeed in reducing the diameter of the paraboloid, the reduced paraboloid structures still occupy large volumes in the launch vehicle, resulting in high costs for each device launched. In addition, the deployment mechanisms of the background art are complex, and thus prone to failure. Where these problems are solved, the deployment requires the services of an astronaut outside the launch vehicle.
Recent attempts to pack a paraboloid accomplish a reduction in diameter. However, the resulting structure nevertheless occupies a large volume in the launch vehicle, and the resulting deployment structure is complex and unreliable. (Palmer, U.S. Pat. No. 4,862,190, issued Aug. 29, 1989). In the Palmer device, the paraboloid is compacted by folding outer panels in an accordion-like fashion in front of a central panel, resulting in a device which, although smaller in diameter, occupies a great deal of space in the launch vehicle. In addition, its many panels remain connected even when compacted through the use of a large number of hinges, each of which lowers the reliability of the system as a whole. Further, it requires a motor for automatic deployment, greatly reducing its reliability. Because of the complexity of the Palmer design, more reliable deployment methods, such as pyrotechnics, cannot be used.
Another attempt (Westphal, U.S. Pat. No. 4,511,901) also collapses into a shape with a smaller radius, but having a large volume. Further, Westphal uses an extremely complex hinge structure which allows both pivoting and rotation simultaneously. The hinge structure as well as the connecting structure makes the Westphal design unreliable as well. Still another attempt reduces the complexity of the design and deployment mechanisms, but fails to achieve a truly compact design. (U.S. patent application Ser. No. 07/751,719, filed Aug. 29, 1991, having the same assignee as the present invention.)
An attempt which succeeds in reducing the volume occupied by the collapsed apparatus nevertheless requires a complex assembly procedure, necessitating the services of an astronaut, and precluding the use of an unmanned rocket as a launch vehicle. (Kaminskas, U.S. Pat. No. 4,811,034). Kaminskas provides a compact structure, but never succeeds in providing a mechanism that is simple enough to deploy automatically.
None of these background art devices simultaneously reduces the diameter of the paraboloid while keeping volume requirements low by the use of a simple, reliable design that is easy to deploy automatically.